Method of galvanizing with molten zinc-aluminum alloy

Abstract

A steel material subjected to preliminary treatments to remove an oxide film on the surface is immersed in a molten flux bath in an independent vessel and thereafter immersed in a molten zinc-aluminum alloy bath in a separate vessel to be galvanized with a coating of the alloy. The molten flux bath consists essentially of 5-25 wt % of an alkali metal chloride, typified by sodium chloride, or an alkaline earth metal, and the balance being zinc chloride. The flux bath may additionally contain 1-5 wt % of an alkali metal fluoride typified by sodium fluoride. The method allows for inexpensive, efficient and one-stage galvanizing with a corrosion-resistant molten zinc alloy of a high aluminum content to produce a smooth, uniform and beautiful galvanized layer on the surfaces of various steel materials.

What is claimed is:  
     
       1. A method of galvanizing with a molten zinc-aluminum alloy comprising immersing an oxide-film free iron or steel material in a molten flux bath in a first vessel, said molten flux bath consisting essentially of 80 to 90 wt % of zinc chloride and 10 to 20 wt % of at least one metal chloride selected from the group consisting of an alkali metal chloride and an alkaline earth metal chloride and optionally an alkali metal fluoride, said molten flux bath being maintained at a temperature of 400 to 560° C., and thereafter immersing the resultant flux coated iron or steel material in a bath containing a molten zinc-aluminum alloy in a second vessel to coat the resultant flux coated iron or steel material with a zinc-aluminum alloy layer, said molten zinc-aluminum alloy being a zinc alloy of a high aluminum content comprising 5-80 wt % aluminum and the balance being zinc and optionally comprising one, or two or more additional elements selected from the group consisting of silicon, magnesium and a rare earth element. 
     
     
       2. The method according to claim  1 , wherein said at least one metal chloride selected from the group consisting of an alkali metal chloride and an alkaline earth metal chloride is an alkali metal chloride which is sodium chloride. 
     
     
       3. The method according to claim  1 , wherein said molten flux bath consists essentially of 80-90 wt % of zinc chloride, 10 to 20 wt % of at least one metal chloride selected from the group consisting of an alkali metal chloride and an alkaline earth metal chloride and 1-5 wt % of an alkali metal fluoride. 
     
     
       4. The method according to claim  3 , wherein said at least one metal chloride selected from the group consisting of an alkali metal chloride and an alkaline earth metal chloride is an alkali metal chloride which is sodium chloride and said alkali metal fluoride is sodium fluoride. 
     
     
       5. The method according to claim  1 , wherein said molten zinc-aluminum alloy is a zinc alloy of a high aluminum content comprising 5 wt % of aluminum. 
     
     
       6. The method according to claim  2 , wherein said molten zinc-aluminum alloy is a zinc alloy of a high aluminum content comprising 5 wt % of aluminum. 
     
     
       7. The method according to claim  3 , wherein said molten zinc-aluminum alloy is a zinc alloy of a high aluminum content comprising 5 wt % of aluminum. 
     
     
       8. The method according to claim  4 , wherein said molten zinc-aluminum alloy is a zinc alloy of a high aluminum content comprising 5 wt % of aluminum. 
     
     
       9. The method according to claim  1 , wherein said molten zinc-aluminum alloy is a zinc alloy of a high aluminum content comprising 55 wt % of aluminum. 
     
     
       10. The method according to claim  2 , wherein said molten zinc-aluminum alloy is a zinc alloy of a high aluminum content comprising 55 wt % of aluminum. 
     
     
       11. The method according to claim  3 , wherein said molten zinc-aluminum alloy is a zinc alloy of a high aluminum content comprising 55 wt % of aluminum. 
     
     
       12. The method according to claim  4 , wherein said molten zinc-aluminum alloy is a zinc alloy of a high aluminum content comprising 55 wt % of aluminum. 
     
     
       13. The method according to claim  1 , wherein the molten flux bath contains 1 to 7 wt % of an alkali metal fluoride selected from the group consisting of sodium fluoride, potassium fluoride and lithium fluoride. 
     
     
       14. The method according to claim  1 , wherein the molten flux bath contains 3 wt % of sodium fluoride. 
     
     
       15. The method according to claim  1 , wherein the zinc chloride is in an amount of 80 wt %. 
     
     
       16. The method according to claim  1 , wherein the zinc chloride is in an amount of 82 wt %. 
     
     
       17. The method according to claim  1 , wherein the zinc chloride is in an amount of 85 wt %. 
     
     
       18. The method according to claim  1 , wherein the zinc chloride is in an amount of 90 wt %.